Catheter-based diagnostic and treatment systems have made possible the exploration and treatment of various bodily vessels and organs. Such catheters are introduced through a vessel leading to the cavity in the target organ, or may alternatively be introduced directly into the organ through an incision made in the wall of the organ. These procedures avoid the trauma to the patient and the extended recuperation times typically associated with an open surgical procedure.
To provide effective diagnosis or therapy, it is frequently necessary to first map the zone to be treated with great precision. Such mapping may be performed, for example, when it is desired to selectively ablate current pathways within a heart to treat atrial fibrillation. Often, the mapping procedure is complicated by difficulties in locating the zone(s) to be treated because of the periodic movements of the heart throughout the cardiac cycle.
Previously-known systems for mapping the interior of a vessel or organ are described, for example, in U.S. Pat. Nos. 6,546,271 and 6,226,542. The catheters described in those patents employ electro-magnetic, magnetic or acoustic sensors to map the position of a distal end of the catheter in space and then construct a three-dimensional visualization of the vessel or organ interior.
One drawback of such previously known mapping systems is that they require manual feedback from the catheter and/or impedance measurements to determine when the catheter is properly positioned relative to the wall of the vessel or organ. Those previously-known systems do not measure contact forces with the vessel or organ wall nor do they detect contact forces applied by the catheter against the organ or vessel wall, which may modify the true location of the wall. Instead, previously known mapping methods are time-consuming, highly dependent upon the skill of the clinician, and are unable to compensate for artifacts created by excessive contact forces.
It therefore would be desirable to provide apparatus and methods for detecting and monitoring contact forces between a mapping catheter and the wall of an organ or vessel, so to enable faster and more accurate mapping. It also would be desirable to provide apparatus and methods that permit the process to be automated, thereby improving registration of measured electro-physiologic values and spatial coordinates, for example, by recording such values only where the contact forces fall within a predetermined range.
Once the topography of the vessel or organ is mapped, either the same or a different catheter may be employed to effect treatment. Depending upon the specific treatment to be applied to the vessel or organ, the catheter may comprise any of a number of end effectors, such as radio frequency ablation electrodes, a rotary cutting head, laser ablation system, injection needle or cryogenic fluid delivery system. Exemplary systems are described, for example, in U.S. Pat. Nos. 6,120,520, 6,102,926, 5,575,787, 5,409,000 and 5,423,807.
Because the effectiveness of such end effectors often depends on having the end effector in contact with the wall of the organ or vessel, many previously-known treatment systems include expandable baskets or hooks that stabilize the extremity of the catheter in contact with the wall. Such arrangements, however, may be inherently imprecise due to the motion of the organ or vessel. Moreover, the previously-known systems do not provide the ability of sense the load applied to the distal extremity of the catheter by movement of the tissue wall.
For example, in the case of a cardiac ablation system, at one extreme the creation of a gap between the end effector of the treatment system and the tissue wall may render the treatment ineffective and inadequately ablate the tissue zone. At the other extreme, if the end effector of the catheter contacts the tissue wall with excessive force, if may inadvertently puncture the tissue, resulting in cardiac tamponade.
In view of the foregoing, it would be desirable to provide a catheter-based diagnostic or treatment system that permits sensing of the load applied to the distal extremity of the catheter, including periodic loads arising from movement of the organ or tissue. It further would be desirable to have a load sensing system coupled to control operation of the end effector, so that the end effector is operated, either manually or automatically, only when the contact force is detected to fall within a predetermined range.
U.S. Pat. No. 6,695,808 proposes several solutions to measure the force vector arising from contact with a tissue surface, including mechanical, capacitive, inductive and resistive pressure sensing devices. One drawback of such devices, however, is that they are relatively complex and must be sealed to prevent blood or other liquids from disturbing the measurements. In addition, such load sensing devices may result in an increase in the insertion profile of the distal extremity of the catheter. Still further, sensors of the types described in that patent may be subject to electromagnetic interference.
One previously-known solution for dealing with potential electromagnetic interference in the medical environment is to use light-based systems rather than electrical measurement systems, such as described in U.S. Pat. No. 6,470,205 to Bosselman. That patent describes a robotic system for performing surgery comprising a series of rigid links coupled by articulated joints. A plurality of Bragg gratings are disposed at the articulated joints so that the bend angle of each joint may be determined optically, for example, by measuring the change in the wavelength of light reflected by the Bragg gratings using an interferometer. Calculation of the bend angles does not require knowledge of the characteristics of the rigid links.
International Publication No. WO 01/33165 to Bucholtz describes an alternative spatial orientation system wherein wavelength changes measured in a triad of optical fiber strain sensors are used to compute the spatial orientation of a catheter or other medical instrument.
An article by J. Peirs et al., entitled “Design of an Optical Force Sensor for Force Feedback during Minimally Invasive Robotic Surgery,” published by Katholieke Universiteit Leuven, Belgium, describes a tri-axial force sensor for use generating force feedback systems in a robotic surgery system. The apparatus includes a plurality of optical fibers that direct light onto a mirrored surface disposed adjacent to a distal tip of the device. The intensity of the light reflected from the mirrored surface is measured and may be correlated to the force required to impose a predetermined amount of flexure to the distal tip. The article describes a flexible and compact structure that supports the mirrored surface and produces variations in light intensity responsive to contact forces that deform the structure.
In view of the drawbacks of the previously known catheters, it would be desirable to provide diagnostic and treatment apparatus, such as a catheter, that permits sensing of loads applied to a distal extremity of the apparatus, but which do not substantially increase the insertion profile of the apparatus.
It further would be desirable to provide diagnostic and treatment apparatus, such as a catheter, that permits the computation of forces applied to a distal extremity of the apparatus, and which is substantially immune to electromagnetic interference.
It also would be desirable to provide a catheter having force-sensing capability that includes a compact and flexible force measurement structure that may be used to modulate reflected light intensities responsive to contact forces arising from contact between a distal end of the catheter and a target organ or vessel.